1. Field of the Invention
The present invention relates to the use of a compound. In particular, the present invention relates to the use of ethylene diaminedisuccinic acid "EDDS".
2. Description of Related Art
In some applications it is desirable to clean metal surfaces, such as in the automotive and aeronautical industries, and in applications such as metal machining and forming, as well as in the preparation of circuit boards and integrated circuits.
Many of the metal cleaning compositions used contain, as their active agents, acids. However, whilst the acids may remove the external layers of dirt, grease, unwanted paint and the like, they can remove some or all of the protective metal oxide layers and, in doing so, make the cleaned metal more prone to corrosion. This is very undesirable.
There is therefore a need to have a metal cleaner that is non-corrosive, i.e. will not remove the metal's protective oxide layer (see for example Business Communications Company Inc. Report C.173 page 20, June 1993).
Generally, the corrosiveness of a solution can be measured in terms of anodic breakdown potential (mV) of the metal oxide layer. The higher the anodic breakdown potential (ABDP), the less the metal will corrode during and after treatment with the metal cleaner.
Ideally, metal cleaners should have ABDP values of at least 200 mV. Preferably, for the cleaning of aluminum it is desirable that the metal cleaners should have ABDP values of at least 400 mV.
Two of the commonly used metal cleaners are ethylene diamine tetra-acetic acid (EDTA) and gluconic acid (GA). However, there are problems associated with these metal cleaners. In this regard, under certain conditions EDTA has an ABDP value of 0 mV for aluminum and copper, two metals which are often in need of cleaning; whereas gluconic acid has an ABDP value of 0 mV for zinc, copper and aluminum.
Further ABDP values for these two metal cleaners are presented later in Tables 1-3.
There is therefore a need for metal cleaners that are not corrosive, i.e. have a low-corrosive effect on the metals.
The present invention seeks to overcome the problems associated with the prior art metal cleaners.